The present invention relates to a new and improved construction of gear grinding machine and method of grinding gear teeth flanks at such machine.
Generally speaking, the gear grinding machine of the invention is of the type comprising a workpiece support and a tool base which are movable relative to one another for partial movements of the workpiece, for setting the gear teeth data, for movements for forming a tooth profile, and for the to-and-fro lengthwise or longitudinal stroke along the tooth flanks to be ground. Additionally, there is provided a grinding wheel support which is pivotably mounted at the tool base for pivotal movement about a pivot axis. A grinding wheel is mounted to be rotatably drivable at the grinding wheel support, the rotational axis of the grinding wheel extending transversely to the pivot axis of the grinding wheel support.
In German Patent Publication No. 2,641,554 applicant has disclosed a gear grinding machine of this species. In that prior art construction two dished or plate-shaped grinding wheels or disks are each mounted at a respective pivotal grinding support or grinding wheel support, for accomplishing simultaneous grinding of a right tooth flank and a left tooth flank. The pivot axis of each grinding wheel support intersects the rotational axis of the related grinding wheel at right angles and extends at least approximately through the grinding point where the grinding wheel contacts the tooth flank and also would still contact the same if the more or less enlarged contact surface between the grinding wheel and the tooth flank, in end section, were reduced to a point with infinite small advance or feed. In order to produce involute-shaped tooth profiles, the heretofore proposed machine is equipped with a generating drive, by means of which there can be accomplished in conventional fashion, a generating motion between the gear to be ground and both of the grinding wheels. The degree of pivoting of both grinding wheel supports solely has the purpose of insuring that both grinding wheels can be adjusted at an inclination in relation to one another and in relation to the generating plane. The once selected setting or adjustment is continuously maintained during grinding of a given tooth profile. According to this prior art proposal the connection line of the grinding points or contact zones of both grinding wheels is continuously maintained during the grinding operation, at such a spacing from the base circle of the gear teeth to be ground that, in each terminal position of the generating movement, one of the grinding wheels machines a tooth tip, and, at the same time, the other grinding wheel machines a tooth root. This setting of the grinding wheels results in the grinding-pressure angle or angle of attack of each grinding wheel continuously changing during the generating movement, and specifically, with a spacing radially within the tangential plane at the base circle, between a maximum at the tooth tip to a minimum at the tooth base and vice-versa, and with a spacing radially externally of the tangential plane at the base circle, between a minimum at the tooth tip to a maximum at the tooth root and vice-versa.
Under the terms "grinding-pressure angle or angle of attack" there is to be understood, just as was the case for the aforementioned prior art patent publication referred to above, and equally of the disclosure of the instant invention, the angle between the tangent at the tooth profile of the workpiece and the planar surface of the grinding wheel.
The continuous change of the grinding-angle of attack affords the advantage that appreciably more grinding grains or granules can participate in the machining or metal removal work than was possible with the older techniques where the grinding wheels or each grinding wheel acted by means of an edge, which had to be maintained sharp at all times, with a fixed grinding-angle of attack at the workpiece. This in effect means that already, according to the heretofore known proposal, the number of grinding grains participating in the grinding work is increased, so that also then when the grinding wheels are relatively seldomly dressed, there is always available a sufficient number of sharp-edged grinding grains, so that there can be removed from the workpiece a multiplicity of small individual chips or cuttings. By virtue of the continuous change of the grinding-angle of attack there is made better use of the pore volume of the grinding wheel for removal of the chips or cuttings. Due to the changing grinding-angle of attack there also is continuously altered the flow angle of the chips or the like. Consequently, there is a lesser danger that the chips will tend to wedge into the pores, which, in turn, has the benefit that there is reduced the danger of grinding wheel burn. Because of the balance effect, associated with the continuously changing grinding-angle of attack, the grinding grains tend to break away before they become excessively dull. This phenomenon leads to the result that, according to the prior art proposal, there can be obtained a higher grinding efficiency and there is reduced the consumption or using up of the grinding wheel which is caused by the dressing work.
According to the heretofore known prior art proposal the change of the grinding-angle of attack, arising during the generating movement between the grinding wheels and workpiece, exclusively is a consequence of the aforementioned spacing between the connection line of the grinding points of both grinding wheels and the base circle of the gear. This spacing cannot be selected to be randomly large, since otherwise the ground tooth profile would deviate, to an undesired degree, from a purely involute profile. Consequently, the advantages of an increased grinding efficiency, which are attributable to changing the grinding-angle of attack during each generating stroke, in other words, an increased volume of material removal per unit of time and a reduced consumption of the grinding wheels per unit of machined workpiece volume, can only be obtained to a limited degree and dependent upon the data of the gear teeth which are to be ground.